| Due to the rapid development of China’s industrialization,industrial pollution problems are increasing day by day,among which industrial sewage treatment and contaminated soil remediation have become an important topic of environmental governance.Microbial remediation has attracted worldwide attention and research because of its advantages of low energy consumption,economic and environmental protection,and recyclable utilization.Most microbial remediation methods are restricted by high temperature,high salinity and other environmental conditions in the practical application,which greatly limits the practical application of microbial adsorbents in industrial wastewater treatment.For the above problems,22 strains of bacteria were isolated from the sediments of deep hydrothermal vent in the South Atlantic Ocean,and the target bacterial strains with high temperature and salt tolerance and good lead resistance were screened out.To explore the adsorption capacity of active and inactivated cells at different conditions.The morphology characterization and chemical composition characterization analysis of the strain 4-2 before and after adsorption was conducted to show the adsorption mechanism under extreme environments and the key substances affecting strain cells to tolerate high temperatures.The main research contents and results are as follows:(1)By measuring the production of extracellular polysaccharides and extracellular proteins of 22 bacterial strains at 25℃ and 55℃,the strains 4-2,B-1,12-1,E-1,M-1 and G-1 with high activity at high temperature were obtained.At the same time,the Pb2+ tolerance of 22 strains was tested,among which strains 3-2A and 4-2 could tolerate 450 mg/L and 500 mg/L Pb2+ concentration,respectively.Combined with the ability of high temperature and heavy metal lead tolerance,Pseudomonas sp.4-2 was identified as the target strain to treat high-temperature lead-containing wastewater.Furthermore,the growth curve of the strain was further measured at different temperatures and salinity.The results showed that the suitable growth temperature of the strain was 15-45℃,and it was difficult to grow in an environment above 65℃.So,strain 4-2 belongs to the facultative thermophilic bacterium,also known as thermoduric bacterium.The optimum salinity for growth is 1-5%,and it is difficult to grow when the salinity is higher than 10%.So,strain 4-2 is also a moderately halophilic bacterium.(2)To investigate the adsorption effect of active and inactivated cells of strain 4-2 under different biosorbent dose,pH,initial concentration of heavy metals,temperature,salinity and adsorption time.The results showed that the optimal adsorption conditions for active cells were pH=6.0,C0=70 mg/L,temperature 55℃,salinity 5%,adsorption time 150 min,Qm 226.24 mg/g at 0.2 g/L cell dosage.The optimum adsorption conditions for inactivated cells were pH=6.,C0=70 mg/L,temperature 35℃,salinity 5%,adsorption time 100 min,Qm 204.91 mg/g.Through the study of extracellular adsorption and intracellular accumulation in the active cells of strain,it was found that only about 10%of Pb2+were accumulated in the cells,and the remaining 90%was on the surface.The adsorption process of active cells of strain 4-2 was spontaneous endothermic reaction at 15-65℃,while that of inactivated cells was spontaneous exothermic reaction at 15-45℃ and spontaneous endothermic reaction at 45-65℃.The adsorption processes had the best fit with Langmuir isotherm model and the pseudo-second-order kinetic model.There were physical adsorption and chemical adsorption,and chemical adsorption was mainly carried out.(3)In order to further explore the adsorption mechanism of strain 4-2 in high temperature and high salinity environment,SEM-EDS,TEM,XRD and XPS analysis showed that PbS and Pb(OH)2 precipitates formed on the surface of strain 4-2 after adsorption.FTIR was used to analyze the main functional groups adsorbed on the bacterial cell surface before and after adsorption,including hydroxyl,carboxyl,amine,sulfonic,amide and alkyl groups.The adsorption process mainly included diffusion,surface adsorption,micro-precipitation,surface complexation and intracellular accumulation(only in living cells).The results of VTIS and 2D-COS analysis showed that the changes of structure were lipids,polysaccharides and proteins in descending order with increasing temperature.The response sequence was proteins,lipids and polysaccharides.The molecular structure of polysaccharides in strain 4-2 may be the main factor affecting the thermal stability and adsorption efficiency at high temperature.In conclusion,Pseudomonas sp.4-2 is a biosorbent with great development potential in extreme environment such as high temperature and high salinity and the exploration of its adsorption and heat resistance mechanism provides a new development idea for the treatment of industrial wastewater by bacteria under extreme conditions. |
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